Assessing safety against derailment of KiwiRail’s push-pull trains

The objective of this paper is to describe the calculations that were carried out by Interfleet Technology (lInterfleetr) to assess the safety against flange climbing derailment for KiwiRailrs SA and SD passenger cars in push-pull operation on the Auckland suburban network. Push-pull trains are prone to encounter train buckling forces when propelled through curves by a locomotive in push mode. The risk of flange climbing derailment can increase with the action of longitudinal traction forces in push mode, as compared to the normal risk level associated with operation in pull mode. The method that was used to assess the safety against flange climbing derailment was first to simulate the effect of tractive lpushr forces applied to an SA/SD train using Working Model (lWMr) motion simulation software, then to apply the forces found in WM to a single vehicle using Vampire dynamic analysis software. WM was used in order to check for train buckling in propelling mode and to calculate the coupler angles and resulting forces on the passenger cars due to the applied tractive effort. Vampire calculations were then made for safety against flange climbing derailment, as these calculations require a detailed representation of the wheel/rail interface. The Vampire calculations used a single-vehicle model of an SA car in tare condition with S-Ride bogies, with external forces applied to the body as found from the preceding WM calculations. The results from the Vampire calculations indicate that SA and SD cars with S-Ride bogies should be safe against derailment on New Zealand track infrastructure with inflated and deflated air suspension, including being propelled by a DFT or DC locomotive in notch 4 or less. The calculations show that the notch 4 restriction is necessary for safe operation in push-mode over the track geometry considered in this study.